DC motor power supply question

[cwickham]

im looking into a dc motor for a project, allot of the more decent DC motors need 130V DC supply, anyone had experience building a supply like that, is it expensive to do?

the motors im looking at are from treadmills if that helps so approx 2hp some times 90v, but most times 130

i could power it with much less voltage then 130 for what im doing, as long as i keep it around 1hp

thanks
craig

 

[Leftyretro]

im looking into a dc motor for a project, allot of the more decent DC motors need 130V DC supply, anyone had experience building a supply like that, is it expensive to do?

the motors im looking at are from treadmills if that helps so approx 2hp some times 90v, but most times 130

thanks
craig

Well 2hp represents around 1,500 watts of power so any power supply designed for that much power does have to be designed carefully and it's component costs will not be "cheap".

Lefty

 

[cwickham]

yeah i figured as much, i should just get an old treadmill and use the motor and supply that comes with it,
that might end up being cheaper, not nearly as fun though

 

[Ubergeek63]

https://www.electro-tech-online.com/custompdfs/2008/12/irfb4332pbf.pdf ($4 at digikey)
https://www.electro-tech-online.com/custompdfs/2008/12/GBJ25005-GBJ2512GBJ.pdf ($2.3)
**broken link removed** ($2.5)
https://www.electro-tech-online.com/custompdfs/2008/12/EE127_UQ_TS_DNE.pdf ($6)

So you can drive the thing for $16 in power parts.

 

[Leftyretro]

https://www.electro-tech-online.com/custompdfs/2008/12/irfb4332pbf-1.pdf ($4 at digikey)
https://www.electro-tech-online.com/custompdfs/2008/12/GBJ25005-GBJ2512GBJ-1.pdf ($2.3)
**broken link removed** ($2.5)
https://www.electro-tech-online.com/custompdfs/2008/12/EE127_UQ_TS_DNE-1.pdf ($6)

So you can drive the thing for $16 in power parts.

Are you proposing direct conversion of AC line power without a isolation transformer to power a 2hp motor?

 

[Diver300]

It is quite common to run motors of that power with no isolation. If the voltage is 130 V, that is about what the mains in the USA is, so you have to be just as careful whether or not there is an isolator.

The treadmill won't have isolators.

If the low voltage control is isolated from the power electronics, it will be done with opto isolators and a low power signal.

 

[Leftyretro]

It is quite common to run motors of that power with no isolation. If the voltage is 130 V, that is about what the mains in the USA is, so you have to be just as careful whether or not there is an isolator.

The treadmill won't have isolators.

If the low voltage control is isolated from the power electronics, it will be done with opto isolators and a low power signal.

I had no doubt it can be made to work, but without seeing a schematic drawing of the complete supply/control circuit, I thought the issue of non isolation was a valid question.

Even home PCs don't use input transformers, but rather directly rectify the AC input voltage followed by a multi-voltage SMPS circuit, so there is a way to design power supplies to be safe and compliant with electrical safety codes, but I would not trust myself to design and build a 1,500 watt without utilizing a input transformer.

Lefty

 

[Ubergeek63]

I had no doubt it can be made to work, but without seeing a schematic drawing of the complete supply/control circuit, I thought the issue of non isolation was a valid question.

Even home PCs don't use input transformers, but rather directly rectify the AC input voltage followed by a multi-voltage SMPS circuit, so there is a way to design power supplies to be safe and compliant with electrical safety codes, but I would not trust myself to design and build a 1,500 watt without utilizing a input transformer.

Lefty

It is done without isolation to the motor. Full safety isolation is only required for use contact surfaces with safety ground being considdered one level of isolation. The only time isolation transformers are required for the motors is for medical patient contact equipment where they put a $300+ med rated iso transformer, and it is more for leakage current to ground being a safety issue with patient contact.

Home PCs actually do have the required isolation in the SPMS transformer, but they are also small fraction of the power.

At any rate, safety regs require grounding and safety isolation up to 5KV (CE medical) to the user from all high voltage (greater than 60V) or power (sorry I do not remember the power level off hand)